Method of producing hydrogen from a carbon monoxide-containing gas stream and heat recovery



G. R. JAMES Dec. 20, 1966 METHOD OF PRODUCING HYDROGEN FROM A CARBONMONOXIDE-CONTAINING GAS STREAM AND HEAT RECOVERY Original Filed Jan. 11.1960 GEORGE RUSSELL JAMES INVENTOR.

AGENT United States Patent 3,292,998 METHOD OF PRODUCING HYDROGEN FROM ACARBON MONOXIDE-CONTAINING GAS STREAM AND HEAT RECOVERY I George RussellJames, Armonk, N.Y., assignor to Chemical Construction Corporation, NewYork, N.Y., a corporation of Delaware Original application Jan. 11,1960, Ser. No. 1,571. Divided and this application Mar. 22, 1963, Ser.No.

2 Claims. (11. 23-213 This invention relates to processes in which heatin the form of latent heat of vaporization is exchanged between gasstreams, with the heated gas stream receiving vaporized liquid while thecooled stream gives up heat mainly through the liquefying of condensablevapor, and is a division of application Ser. No. 1,571 filed Jan. 11,1960, and now abandoned. A process and apparatus for performing theprocess has been devised, which provides improved process efliciency andmore economical transfer of heat. More sepcifically, the process relatesto the preparation of gas for the catalytic reaction of carbon monoxidewith water vapor to produce hydrogen. The process of the presentinvention provides improved heat economy and steam savings in connectionwith the required addition of water vapor to the process gas stream.

Numerous industrial processes require the addition of a vapor componentto a gas stream prior to reaction at elevated temperature. Where thevapor component is generated from a Liquid source, thermal requirementsin producing the vapor are usually an important consideration in theoverall efficiency of the process. Where the final gas stream afterreaction contains a significant proportion of unreacted vapor,separation of this vapor is usually accomplished by cooling and lowtemperature condensation, and since the latent heat of vaporization isonly available at a relatively low temperature, this heat is usuallywasted. A typical process of this nature is the production of hydrogenfrom gas streams containing carbon monoxide, by catalytic reaction ofthe carbon monoxide with water vapor at an elevated temperature. Adetailed discussion of the standard aspects of this process appears inan article published in Chemical and Metallurgical Engineering v. 43, #3(March 1936), p. 122-126.

In this process as usually practiced, the incoming cold gas stream iscontacted with a stream of hot water flowing countercurrently in apacked tower. As a result the gas stream is warmed and in addition therequired amount of water vapor is added to the gas stream by evaporationof some of the hot liquid water. The humiditied and warmed gas stream isthen further heated in conventional heat exchangers, and is passedthrough one or more stages of catalytic reaction. The resulting hotproduct gas stream is then cooled and a portion of the residualunreacted water vapor contained therein is removed, by passing the gasstream through a second packed tower countercurrent to a stream of coolwater. This cool water stream is preferably obtained as the residualwater stream from the first tower, and the resulting hot water streamobtained from the second tower is recycled to the first tower. Thus acirculating liquid water circuit is maintained between the two towers,at two ternperature levels. It is evident that this conventional systemrequires considerable expensive equipment for the alternatehumidification and dehumidification, namely, two packed towers andassociated pumps and piping.

Various other modified systems of heat recovery are described in US.Patents 2,829,113, 2,465,235 and 1,614,072. In these patents thesensible heat available in the reacted gas stream is partially recoveredat a 3,292,998 Patented Dec. 20, 1966 "ice relatively higher temperaturelevel :by heat exchange with liquid water. However, the low temperaturelevel heat, principally latent heat of vaporization derived bycondensation of excess water vapor, is essentially wasted.

Numerous other industrial processes involve condensation of vapor firoma gas stream by cooling, and in many instances the teaching of thepresent invention is applicable as a means of effecting considerablesavings in net heat requirements, whenever vapor is to 'be added to asecond gas stream. Thus, for example, the gasification of hydrocarbonoils involving high temperature generation and quench cooling, producesa hot wet gas which is saturated with water vapor and contains entrainedsolid particles and also possibly contains tars and resins. The usualprocedure is to cool and scrub this gas stream using water. This step'also condenses considerable water vapor from the gas stream. Theresulting stream of hot dirty water is discarded, and consequentlyconsiderable heat is lost, especially 'latent heat of vaporization. Thegas stream is then further cooled and passed to sulfur removal.Subsequent to sulfur removal the gas stream is reheated and steam isadded prior to further process treatment. Obviously this sequence ofprocess steps involves considerable loss of heat.

In the present invention an apparatus and procedure is provided whichproduces a simultaneous cooling of a gas stream and condensationtherefrom of condensable vapor, while in heat exchange with a second gasstream which is heated and to which a sec-0nd vapor is added byintroducing liquid to 'be evaporated on the heat exchange surface. Theapparatus of the present invention is readily distinguished from knownshell vand tube heat exchangers, since the shell side bafiies areemployed to disperse liquid being evaporated onto the outer surface ofthe tubes.

It is an object of the present invention to effect latent heat exchangebetween gas streams.

Another object is to recover in a more eflicient manner the latent heatof vaporization available from condensable vapors .in gas streams.

A further object is to provide more elfective apparatus foraccomplishing latent heat exchange between gas streams.

Still another object is to provide an improved process for the catalyticproduction of hydrogen from carbon monoxide and water vapor, withimproved thermal efiiciency and conversion of available heat.

An additional object .is to more efiiciently add vapor to a gas streamby vaporizing liquid using latent heat of vaporization of condensingvapor from another gas stream.

Another object is to provide a process and apparatus suitable for heatrecovery from gas streams by vapor condensation which permits suchrecovery when the gas stream contains entained solid particles.

These and other objects of the present invention will be evident fromthe description which follows.

Referring to the figure, vessel 1 is a container in which the exchangeof latent heat takes place. If one or both gas streams are at highpressure, vessel 1 may be provided with a high pressure closure such ascover 2. Vessel 1 is divided into sections by partitions 3 and 4, whichare provided with openings which are connected by ducts 5 and 6.Although only two ducts are shown in the figure, this is merely forillustrative purposes. It should be borne in mind that it is within .thescope of this invention to incorporate within vessel 1 any suitablenumber of ducts to provide optimum performance. The colder gas stream 7which is to be warmed and into which liquid is to be vaporized, isadmitted via opening 8 into vessel 1 in the section between partitions 3and 4 and external to ducts 5 and 6. The liquid stream 9 to be vaporizedinto stream -7 is admitted via inlet means 10 and 11 onto gas baflles 12and 13. These gas bafiles extend part way across the central section ofvessel 1 and external to ducts and 6, in such a manner as to direct thegas stream 7 in a flow path as shown by the arrows, substantiallytransverse to ducts 5 and 6. The gas bafiles have the additionalfunction of distributing liquid admitted via and 11 onto the outersurface of ducts 5 and 6. Two battles are shown in the figure, but oneor more than two could be used depending on the size of the vessel 1 andthe volume of gas to be humidified per unit of time. Retention andhorizontal flow of liquid is maintained by lips such as 14, over whichany excess of liquid may flow to the next lower baflle. The main flow ofliquid, however, is across the gas :bafiies and over weirs such as 15 orother distributing means which serve to evenly distribute the liquidonto the outer surface of ducts 5 and 6. In some cases the weirs may beomitted, as for example,when it is desired to essentially flood thewetted surface. In these cases a considerable excess of liquid would beadmitted onto baflles 12 and 13, greater than could be evaporated.Residual liquid would then accumulate above partition 4 and would beremoved or recycled by suitable means.

The liquid film flowing down the outer surface of ducts 5 and 6 receivesheat from the stream inside the ducts, and is vaporized. The hot vaporsjoin the gas stream 7, which is also heated. A final exit gas stream 16which is warm and contains the added vapor component is removed viaopening 17.

The heating effect is produced by obtaining heat, principally latentheat of vaporization, from a hot vaporladen gas stream 18 which isadmitted via opening 19 into vessel 1 in the upper section thereofbetween cover 2 and partition 3. The gas stream '18 then flows downwardsinside ducts 5 and 6, and is cooled with resulting condensation ofliquid derived from the vapor in the gas stream. Depending on flowvelocity considerations, some liquid may form in the ducts within thegas stream. However, the principal amount of condensation will occur onthe inner walls of ductsv 5 and 6. Thus condensed liquid will flow downthe inside walls of ducts 5 and 6. The simultaneous flow of liquid onboth heat transfer surfaces, which consist of the inner and outersurfaces of ducts 5 and 6, is an important aspect of the presentinvention to be discussed infra.

The cooled gas stream is removed from the bottom section of vessel 1 viaopenings 24 as stream 25. The condensed liquid collects in the bottom ofvessel 1 as pool 20, and is removed as required via line 21, valve 22and line 23. In some cases, provided that no impurities are present,line 23 may join line 9 thus adding the hot condensate to the shell sideof vessel 1 for revaporization.

This invent-ion offers numerous advantages as compared with practice inthe prior art, particularly in the case of carbon monoxide reaction withwater vapor to produce hydrogen. The apparatus of the present inventionis much simpler and more economical, since a single unit is providedrather than two packed towers and associated pumps and piping. Ofparticular importance is the fact that much higher heat recovery isachieved, since closer temperature approaches are achieved with higherevaporation on the liquid vaporizing side of the unit. Itis believedthat a major factor in producing the improved heat economy is thesimultaneous flow of liquid on the inner and outer surfaces of theducts. Apparently the flowing liquid films effectively reduce gas filmresistance to heat transfer to a negligible factor in the overallsituation. It will be readily understood by those skilled in the artthat gas film resistance to heat transfer is a major consideration inheat exchange processes. An additional advantage of the presentinvention is the fact that the hot gas is passed inside the ducts.Consequently, any deposit of solids or sludge is readily eliminated fromthe unit.

carbon monoxide reaction with water vapor, whereby hydrogen is produced.An example of such a situation will now be described.

Example I Atypical example of a gas stream containing carbon monoxidewhich is processed by the present invention is the off-gas derived fromacetylene synthesis, after removal of acetylene and other values. Theresidual gas stream is rich in carbon monoxide and is recovered as acool dry gas, typically at F. and p.s.i.g. This gas stream was warmed to280 F. and saturated with from about 280 F. to about 500 F. This hot gasstream was in turn cooled by passing through the ducts of the apparatusof the present invention, and a major proportion of Water vapor thereinwas condensed to. liquid water. was recovered at 235 F. and 88 p.s.i.g.and passed to. further treatment including carbon dioxide removal. Inthis particular process, operating temperatures fluctuated over a rangeof about 30 F., particularly the cool olfgas which varied in originaltemperature from 70 F. to 100 F., depending on prior processingtemperature conditions. Corresponding variations thus occurred, but to alesser degree, in the other gas temperatures. Thus the final cooledconverted gas was recovered at temperatures ranging from about 220 F. to245 F.

The importance of recovery of latent heat of vaporization by theteaching of the present invention is shown by facts relative to theaforementioned example. It was determined that 'B.t.u.s of heatrecovered in cooling the hot gas from 500 F. to 270 F., a temperaturerange of 230 over which only sensible heat was removed without vaporcondensation, was equalled by the heat recovered over the next 9 ofcooling from 270 F. to 261 F., a range in which vapor condensation tookplace. Actually the great bulk of heat recovery was achieved over thelower range of the cooling from 270 to 235: F., during which vaporcondensation was taking place. Thus the process of the above examplewill result in recovery of a relatively large quantity of heat with anylower input hot gas temperature above 280 F., for the Hence it ispossible by the.

aforementioned reasons. teaching of the present invention to use thesensible heat in the output gas, which is available at a high tempera- Isure and temperature will suitably be inlet pressure range of between 15p.s.i.g. to 500 p.s.i.g. and hot gas inlet temperature of about 250 F.to 600 F. with corresponding cold gas outlet temperature at a suitablelower value preferably between about 200 F. .to 450 F., so as to.achieve acceptable heat transfer and liquid vaporization rates withinthe unit.

Other applications of the present invention are shown in the followingexamples.

This factor is quite important in such situations as the cooling of gasstreams derived from hydrocarbon gasification, as discussed supra.

A preferred embodiment of the present invention involves application ofthe concept to the art of catalytic.

The final cooled converted gas stream Example II The utility of thepresent invention in hydrocarbon gasification processes was shown in anapplication involving the hot gas, saturated with water vapor, which isproduced by the gas generator followed by the water quench unit. Thisgas stream, also containing solid carbon particles, was cooled in a heatrecovery unit of the present invention. The result-ing stream of dirtycondensate water was readily removed without plugging the apparatus. Thehot gas was admitted to the unit at 395 F. and 400 p.s.i. g., andremoved at 350 F. and passed to sulfur removal.

The gas stream was received after sulfur removal as a relatively dry gaswith a temperature of 240 F. This gas was then heated and humidified inthe apparatus, and passed to further treatment at 380 F. and 385p.s.i.g. Thus by the method and apparatus of the present invention, thesulfurfree 'gas stream was heated and humidified at negligible cost,since in .the prior art as discussed supra the recovery of heat firomthe hot dirty generator gas has usually not been completely achieved,with required cooling being accomplished by water scrub with dischargeof the resulting dirty warm water to waste.

Example III The present invention was applied to a conventional hydrogenprocess in which essentially all carbon mouoxide in a gas stream isconverted to hydrogen. The conventional hydrocarbon reform steps wereemployed, namely, primary and secondary reform followed by cooling in awaste heat boiler, to react methane with steam and oxygen and produce aprocess gas stream comprising carbon monoxide, water vapor and hydrogenat 800 F. The gas stream was passed through the first stage of carbonmonoxide conversion to produce more hydrogen. The exit gas stream at 850F. was then partially cooled to 450 F. in a gas to gas preheater, andfurther cooled to 240 F. in the reboiler of a regenerator which wasemployed in the carbon dioxide absorption process. The gas stream, nowsaturated with water vapor, was passed through an apparatus unit of thepresent invention and cooled from 240 F. to 200 F. at about 70 psig.Although the temperature drop was comparatively small, a large quantityof heat was removed due to condensation of water vapor from the gasstream.

The gas stream was then cooled further in a conventional heat exchanger,and finally passed to the carbon dioxide absorber where carbon dioxidewas absorbed in a scrubbing solution. The resulting cool gas stream,consisting principally of hydrogen together with a small quantity ofcarbon monoxide, was then warmed fi'om 100 F. to 232 F. and humidifiedin the aforementioned apparatus unit of the present invention. The hotsaturated gas was finally passed to the gas to gas preheater prior tothe second stage of carbon monoxide conversion.

The present invention should not be restricted to the processingdescribed supra, since numerous variations within the scope of thepresent invention will occur to those skilled in the art. Thus forexample, in some cases the hot condensate water recovered from the gasbeing cooled and withdrawn at the bottom of the unit will be quiteclean, and all or a portion of this hot water could be utilized tofurnish the liquid stream being fed to the gas battles for evaporationon the cold gas side of the unit. In other instances such as in heatrecovery from dirty gas produced by hydrocarbon gasification, thecondensate stream which is produced by cooling the gas stream will becontaminated, and at best could be utilized in a heat exchanger toindirectly warm the incoming liquid being fed to the gas baffles.

It should be noted that the apparatus may be operated with the hot gasesin and out at the bottom rather than the top. This arrangement wouldresult in recovery of a hotter condensate from the hot gas stream beingcooled. However, a limiting factor in such a procedure is gas flowvelocity, since an excessively high gas velocity could result incarryover of condensed liquid up through the tubes.

Finally, the present invention is 'appiicable to cases where transfer oflatent heat is to occur [between two different liquids which must bemaintained separate from each other.

What I claim is:

1. In the process of catalytic reaction of carbon mon oxide in a feedgas stream with water vapor at a temperature in the range of about 800F. to 850 F. to produce a hot product gas stream principally containinghydrogen, carbon dioxide and excess unreacted water vapor, the method ofheat recovery by transfer of latent heat derived from water vaporcondensation which comprises passing said feed gas stream at a pressureof between about 15 p.s.i. g. to 500 psig in contact with a film ofliquid water flowing downwards on the outer surface of a verticallyoriented duct, said feed gas stream flowing generally upwardscountercurrent to said liquid water film, and vaporizing said liquidwater fii-m by concurrently passing said hot product gas streamprecooled to a temperature in the range of about 250 F. to 600 F.downwards through said duct, whereby said feed gas stream is heated to atemperature of between about 200 F. to 450 F. and water vapor isincorporated therein catalytical ly reacting carbon monoxide in saidfeed gas stream with water vapor, partially cooling the resulting hotproduct gas stream to a temperature in the range of about 250 F. to 600F., and vaporizing said liquid water film as aforesaid by passing thepartially cooled product gas stream downwards through said duct, andthereby further cooling said partially cooled product gas stream to alower temperature in the range from about 200 F. to less than 270 F. andcondensing water vapor from said product gas stream, whereby the latentheat of condensation from said condensing water vapor is transferredthrough said duct to said liquid water film being vaporized into saidfeed gas stream.

2. In the process of catalytically reacting the carbon monoxide contentof a residual off-gas stream derived from acetylene manufacture withwater vapor at elevated temperature to produce a hot product gas streamprincipally containing hydrogen, carbon dioxide and excess unreactedwater vapor, the method of heat recovery by transfer of latent heatderived from water vapor condensation which comprises contacting saidresidual olfgas stream at a pressure in the range of about 15 -p.s.i.-g.to 500 p.s.i.g. and initial temperature of between about 70 F. to F.with a film of liquid water flowing downwards on the outer surface of avertically oriented iduct, said residual ofl-gas stream flowinggenerally upwards countercurrent to said liquid water film, andvaporizing said liquid water film by concurrently passing said hotproduct gas stream precooled to a temperature in the range of about 280F. to 500 F. downwards through said duct, whereby said residual off-gasstream is heated and water vapor is incorporated therein, catalyticallyreacting carbon monoxide in said residual off-gas stream with watervapor, partially cooling the resulting hot product gas stream to atemperature in the range of about 280 F. to 500 F., and vaporizing saidliquid water film as aforesaid by passing the partially cooled productgas stream downwards through said duct, and thereby further cooling saidpartially cooled product gas stream to a lower temperature of betweenabout 220 F. to 245 F. and condensing water vapor from said product gasstream, and transferring the latent heat of condensation of saidcondensing Water vapor through said duct to said liquid water film beingvaporized into said residual oif-gas stream.

(References on following page) P-atalrt 23-213 Scherer 261-153 XHaldeman 261-453 Simonek et a1. 23-213 Eickmeyer 1651 18 X 1/1930 GreatBritain. 9 /1950 Italy.

6 OSCAR R. VERTI Z, Primary Examiner.

1. IN THE PROCESS OF CATALYTIC REACTION OF CARBON MONOXIDE IN A FEED GASSTREAM WITH WATER VAPOR AT A TEMPERATURE IN THE RANGE OF ABOUT 850*F. TO850*F. TO PRODUCE A HOT PRODUCT GAS STREAM PRINCIPALLY CONTAININGHYDROGEN, CARBON DIOXIDE AND EXCESS UNREACTED WATER VAPOR, THE METHOD OFHEAT RECOVERY BY TRANSFER OF LATENT HEAT DERIVED FROM WATER VAPORCONDENSATION WHICH COMPRISES PASSING SAID FEED GAS STREAM AT ATEMPERATURE OF BETWEEN ABOUT 15 P.S.I.G. TO 500 P.S.I.G. IN CONTACT WITHA FILM OF LIQUID WATER FLOWING DOWNWARDS ON THE OUTER SURFACE OF AVERTICALLY ORIENTED DUCT, SAID FEED GAS STREAM FLOWING GENERALLY UPWARDSCOUNTERCURRENT TO SAID LIQUID WATER FILM, AND VAPORIZING SAID LIQUIDWATER FILM BY CONCURRENTLY PASSING SAID HOT PRODUCT GAS STREAM PRECOOLEDTO A TEMPERATURE IN THE RANGE OF ABOUT 250*F. TO 600*F. DOWNWARDSTHROUGH SAID DUCT, WHEREBY SAID FEED GAS STREAM IS HEATED TO ATEMPERATURE OF BETWEEN ABOUT 200* F. TO 450*F. AND WATER VAPOR ISINCORPORATED THEREIN CATALYTICALLY REACTING CARBON MONOXIDE IN SAID FEEDGAS STREAM WITH WATER VAPOR, PARTIALLY COOLING THE RESULTING HOT PRODUCTGAS STREAM TO A TEMPERATURE IN THE RANGE OF ABOUT 250*F. TO 600*F., ANDVAPORIZING SAID LIQUID WATER FILM AS AFORSIDE BY PASSING THE PARTIALLYCOOLED PRODUCT GAS STREAM DOWNWARDS THROUGH SAID DUCT, AND THEREBYFURTHER COOLING SAID PARTIALLY COOLED PRODUCT GAS STREAM TO A LOWERTEMPERATURE IN THE RANGE FROM ABOUT 200*F. TO LESS THAN 270*F. ANDCONDENSING WATER VAPOR FROM SAID PRODUCT GAS STREAM, WHEREBY THE LATENTHEAT OF CONDENSATION FROM SAID CONDENSING WATER VAPOR IS TRANSFERREDTHROUGH SAID DUCT TO SAID LIQUID WATER FILM BEING VAPORIZED INTO SAIDFEED GAS STREAM.